DESCRIPTION (adapted from application abstract): African trypanosomes are protozoan parasites that cause African trypanosomiasis, a deadly disease with devastating health and economic consequences. The long-term goal of the proposed research is to advance our understanding of two vital components of the cellular architecture of these pathogens: the microtubule cytoskeleton, and the flagellar pocket, a specialized organelle that plays a critical role in host-parasite communication. Both of these structures are required for parasite survival in their mammalian host and insect vector, and are considered to be prime targets for therapeutic intervention in trypanosomiasis. We have shown that a protein called TLTF is localized to the cytoplasmic face of the anterior flagellar pocket membrane in trypanosome protein extracts and a related human protein associates with microtubules in mammalian cells. The first two aims of the proposed research are to utilize combined in vivo and in vitro microtubule binding assays to determine whether these two proteins are bona fide microtubule-binding proteins, and to determine whether or not microtubules contribute to targeting of TLTF in trypanosomes. Another aim of this research is to use biochemical and molecular biological approaches to determine whether the relationship between two anti- TLTF cross-reactive proteins that are present in insect-form trypanosomes. Expression of one of these proteins exhibits dramatic developmental regulation, suggesting that this protein has developmental stage-specific functions. Analysis of point mutations in the TLTF targeting domain suggests that specific protein-protein interactions at the flagellar pocket are important for proper targeting of TLTF. Hence, another aim of this research is to use co-immunoprecipitation and affinity capture resins to determine whether TLTF interacts with other trypanosomal proteins, i.e, whether some TLTF `binding partners` may be components of the flagellar pocket. In addition to contribution to our understanding of the cell biology of a medically important pathogen, the closely related properties of TLTF and a previously uncharacterized human protein make it likely that findings from these studies will have broad biological relevance in other systems.